The present invention relates to an apparatus for and a method of mixing a plurality of materials, specifically powders, in particular components of a pharmaceutical composition, into a mixture having a required homogeneity.
The mixing of pharmaceutical compositions is a crucial step in processing an active drug into a form for administration to a recipient. Pharmaceutical compositions consist of a number of separate components, including the active drug, which must be mixed into a homogeneous mixture to ensure that the appropriate dosage of the active drug is delivered to the recipient.
The concentration of the non-active components in a pharmaceutical mixture is also important since it determines the physical properties of the mixture, such as the rate of dissolution of a tablet in a recipient""s stomach.
One prior art apparatus for mixing the components of a pharmaceutical composition into a homogeneous mixture is known from EP-B-0 631 810. This known apparatus comprises a container, in which the mixture is being prepared by continuously rotating the container. A spectroscopic measuring device is arranged for in-line measurement of the homogeneity of the mixture being prepared in the rotating container. The measuring device has a probe that enters the container through an aperture coinciding with the axis of rotation of the container.
One major disadvantage of this prior-art apparatus is the limited access to the interior of the container. Thus, there is little freedom for finding optimised positions for in-line monitoring. For example, in all types of powder blenders there is a risk for having local zones that are either stagnant or where mixing is less efficient than in other positions in the blender. Thus, the monitored homogeneity on the axis of rotation might not be representative of the actual homogeneity of the mixture in the container. Further, the prior art apparatus is undesirably complicated in construction.
SU-A-1 402 856 discloses an apparatus for mixing thermo-chromic compositions, such as mixtures of cholesteric liquid crystals. The ingredients are fed 10 a stationary container provided with a central stirrer. A thin layer of the mixture is allowed to pass between an interior plate and a window of the container. By inducing temperature gradients in this layer, by means of heaters, the degree of homogeneity is determined by analysis of the colour-temperature characteristics observed at the window. This type of apparatus is unsuitable for monitoring the homogeneity of most substances, and in particular pharmaceutical compositions and the like.
The object of the invention is to find a solution to the above described problems.
This object is achieved by an apparatus and a method according to the accompanying independent claims. Preferred embodiments are set forth in the dependent claims.
With the inventive technique, the measuring device can be arranged to monitor the homogeneity of the mixture at any location in the vessel. The non-rotating vessel provides for ease of attachment of the measuring devices to the vessel. Also, the measurements can be made non-invasively, i.e. without affecting the materials being mixed. Further, the homogeneity of the mixture can be monitored at any desired number of locations simultaneously. This will provide for a more optimised measurement, which will gives a better picture of the actual status of mixing process in the vessel, both with respect to local inhomogeneities as well as to a weighted average measure of the homogeneity in the entire batch.